1. Field of the Invention
The invention relates to a blasting method for cleaning pipes, and to a device which is suitable for carrying out this method.
2. Description of the Related Art
Blasting devices are generally used to clean surfaces with the aid of a mostly gaseous blasting medium to which an abrasive blasting means such as sand or the like can be added. It is also known to use dry ice or dry snow as blasting means (DE-A-195 35 557). The use of dry ice has the advantage that the materials to be cleaned off and subsequently disposed of are not increased by additional blasting means, since dry ice evaporates after use.
The dry ice exerts a cleaning effect through:
1. Thermal shock-induced embrittlement of the material to be cleaned off, accompanied by crack formation (thermal stresses).
2. Penetration of particles into the cracks, produced by thermal stresses, in the materials to be cleaned off, followed by a sudden increase in the volume of the particles during the transition to the gaseous state (sublimation), which leads to `blasting off` the materials to be cleaned off.
3. Kinetic energy when the particles strike the materials to be cleaned off at high speed.
With regard to quick and economic cleaning of relatively large surfaces, it is desirable for the jet produced by the blasting nozzle to be as widely fanned out as possible. Known for this purpose are flat nozzles which produce a jet widened in a fan-like fashion. However, there is still a disadvantage in using abrasive blasting means in that the particles of the blasting means impinge on the tapering walls of the nozzle, with the result that either there is an increased wear at the nozzle or, in the case of dry ice, the particles of the blasting means are smashed into finer particles which no longer have any appreciable abrasive effect.
U.S. Pat. No. 5,664,992 discloses a blasting method in which the blasting nozzle is at first tapered and then expands again, so that an acceleration of the blasting medium is achieved. A spindle-shaped deflecting member is moved through the pipe together with the blasting nozzle and deflects the abrasive blasting means onto the pipe wall.